In message , K
writes
Tim C. writes
Following up to "Martin Brown" :

It used to be used as an insecticide in the old days..

and still is, from the point of view of the tobacco plant itself. ;-)

This has always puzzled me. I assume most of Nicotiana contain
nicotine? - or is it just the tobacco plant itself? Nicotiana
sylvestris, for example, is a magnet for whitefly. Its main defence
seems to be the stickiness of its leaves, but it doesn't protect very
well - the heavy infestation that it attracts causes real damage.

The amount, at least, will vary between species. I presume that
Nicotiana tabacum produces more nicotine that the general run of
species. Furthermore, it is likely that commercial varieties have been
selected for greater production of nicotine.

Apart from that, poisonous plants often get heavy infestations of the
few insects that have adapted to the poisons. (E.g. ragweed and cinnabar
moth.)
--
Stewart Robert Hinsley